Conventional arrangements for carrying out combustion in industrial furnaces are shown in FIGS. 5 and 6. In FIG. 5, a fuel supply portion having laterally opening delivery ports at the delivery end thereof is positioned within an air supply portion b so that air is supplied along the entire periphery of the fuel supply portion. The fuel and air supplied as indicated by arrows from the respective supply portions a and b are mixed in a ceramic burner nozzle c to burn and generate a flame. In this combustion arrangement, since the area near the base of the flame which has the highest rate of combustion and also the highest temperature is surrounded by a thermally insulating wall constituted by the burner nozzle c, radial heat dissipation does not occur, and a large volume of NOx is generated by the high temperature flame, which is disadvantageous.
A combustion arrangement actually applied to a glass melting furnace is shown in FIG. 6. In this arrangement, an air supply portion b and a fuel supply portion a open directly into a furnace chamber d, but since there is little clearance between the surface e of the glass and the air supply portion b, gas recirculating currents are not formed in the furnace, and the air current simply flows along the glass surface e. Since the fuel is directly injected into the air current, the combustion product in the furnace is not mixed with the fuel or air, and therefore combustion at a low oxygen concentration does not occur, which inevitably raises the flame temperature. Thus, the NOx emission level is naturally high, which is disadvantageous.